In FM stereo broadcasting, an FM transmitter produces and transmits a stereo signal which contains a left-hand audio signal and a right-hand audio signal among various other frequency components. Stereo receivers recover the encoded stereo signal from a frequency modulated carrier and decode the stereo signal to recreate the left-hand audio and right-hand audio signals. Typically, the components of the encoded stereo signal are provided by filters as noted in Principles of Communication Systems by Herbert Taub and Donald L. Schilling (McGraw-Hill Book Company, 1971, pages 146-151). Included in the components of the encoded signal is a pilot carrier signal, a waveform proportional to the sum of the left-hand and right-hand audio signals, and a double-sideband suppressed-carrier waveform proportional to the difference of the left-hand and right-hand audio signals. The pilot carrier signal may be easily filtered and modified to recreate a subcarrier frequency which allows synchronous demodulation of the double sideband suppressed-carrier waveform to provide a difference waveform. A baseband filter provides a sum waveform so that the sum and difference signals may be respectively added and subtracted to decode the left-hand audio and right-hand audio signals.
Previous FM stereo decoders have typically been implemented with analog circuitry. When FM stereo receivers are implemented with analog circuitry, frequency drifts associated with changing age of the circuitry and temperature variations cause the quality of reception to vary. Further, analog FM receivers typically have a plurality of filters associated therewith for implementing the various frequency translations required to decode an FM signal as described above.